This application claims the priority of German patent document No. 103 51 715.4, filed Nov. 5, 2003, the disclosure of which is expressly incorporated by reference herein.
The invention relates to an injection head for a liquid-propelled rocket engine.
Known injection heads for liquid-propelled rocket engines have a number of first injection bores for injecting jets of a first propellant constituent into the combustion chamber of a rocket engine, and a number of second injection bores for injecting jets of a second propellant constituent into the combustion chamber, such that the propellant constituents are mixed.
The injection head of the rocket engine must ensure a complete combustion of the propellant with a low combustion chamber volume by effective mixture processing, and must provide a homogeneous combustion gas mixture, a high combustion stability, and, if possible, low injection pressure losses. Furthermore, unacceptably high heat entry at the walls of the combustion chamber and the engine nozzle are to be avoided. Finally, the manufacturing costs should be minimized.
“Rocket Propulsion Elements” by George P. Sutton, Oscar Biblarz, Seventh Edition, Pages 271 to 276, discloses different types of injection heads for liquid-propelled rocket engines, including those which operate according to coaxial, swirl, or oblique jet injection methods. These types of injection heads have the disadvantage that propellant strands can form in the combustion chamber, in which either a rich combustion predominates due to an excess of fuel, or a lean combustion predominates as a result of an oxidation excess. On the one hand, such a strand formation impairs the combustion degree (that is, the efficiency factor of the combustion), while on the other hand, lean strands may lead to hot-gas corrosion or to spot-type excess temperatures—so-called “hot spots”—on the combustion-chamber walls, which can destroy the combustion chamber. If a thermally decomposable fuel is involved, strands with an excess of fuel may lead to local pressure peaks, which can cause high-frequency combustion instabilities.
In one of the oldest configurations, the injection heads operate according to the so-called parallel-jet spray-head injection method. These can supply a strand-free uniform mixture formation of the oxidizer and the fuel in the axial direction (that is, in the direction of the flow of the combustion gases), as well as in the radial direction, thus transversely thereto. In this case, arrangements are known in which the injection bores for the fuel or the oxidizer are alternately arranged in a checkerboard shape, in a circular shape or in a honeycomb shape. However, one disadvantage of known parallel-jet spray-head adjusting heads is that fairly large combustion chamber lengths are required to achieve high combustion efficiency and high capacity. This is essentially because, due to the parallel injection of the fuel and the oxidizer, both constituents come in contact only gradually; thus their reaction takes place only after a relatively long distance.
One object of the present invention is to provide an injection head for a liquid-propelled rocket engine which makes it possible to achieve complete, uniform and stable combustion, even at a short combustion chamber length.
This and other objects and advantages are achieved by the liquid propellant injection head according to the invention, which has a number of first injection bores and a number of second injection bores for injecting propellant jets of a first propellant constituent and of a second propellant constituent respectively into the combustion chamber of the rocket engine with the mutual mixing of the propellant constituents. According to the invention, the first injection bores inject jets of the first propellant constituent with a high impulse, while the second injection bores inject jets of the second propellant constituent with a low impulse. In addition, the first and second injection bores are arranged with respect to one another such that an admixing of the second propellant constituent with the first propellant constituent takes place with an ejector effect of the propellant jets of the first propellant constituent leaving the first injection bores.
One advantage of the injection head according to the invention is that, by parallel injection of the two propellant constituents (and thus of the propellant and the oxidizer), the propellants typically are not mixed in the liquid phase, but not before the gaseous phase, so that high-frequency combustion instabilities are avoided. Another advantage is that the quality of the injection head is relatively insensitive to manufacturing tolerances at the individual injection bores; that is, due to the large number of injection bores, a variation in dimension of individual bores plays only a subordinate role in the composite, and is therefore usually negligible. This is advantageous with respect to expenditures and costs of the manufacturing.
Another important advantage of the injection head according to the invention is that it can achieve a high combustion efficiency of the liquid-propelled rocket engine, due to a high characteristic velocity and thus a high specific output of the engine. Finally, because of a lower susceptibility to dot-type overheating, the operating range of the rocket engine can be considerably expanded. Thus, in comparison to other injection methods, the engine can still be operated in an absolutely stable manner, even with significantly lower injection pressures.
In a preferred embodiment of the invention, the first injection bores have a small flow cross-section for generating the propellant jets of the first propellant constituent with a high impulse, and the second injection bores have a large flow cross-section, for generating the propellant jets of the second propellant constituent with a low impulse.
Preferably, the first injections bores and the second injection bores lead out at the surface of an injection plate bounding the injection head on the combustion chamber side. In a particularly preferred embodiment of the injection head according to the invention, the second injection bores on the surface of the injection plate have a first area with a large flow cross-section for generating the propellant jets of the second propellant constituent with a low impulse, and, upstream with respect to the flow direction of the second propellant constituent, a second area with a small flow cross-section. The second area with the small flow cross-section in the second injection bores is advantageously used to generate a large injection pressure difference, benefiting the hydraulic uncoupling of the propellant delivery system and the combustion chamber.
The injection bores are preferably arranged with their axes parallel to one another.
According to a preferred embodiment of the invention, the first injection bores and the second injection bores are arranged alternately, and optionally.
Alternatively, they may be arranged alternately in a circular manner, or in a honeycomb-shaped manner.
Advantageously the first injection bores have a diameter of from 0.05 to 0.5 mm (preferably from 0.05 to 0.15 mm), while the second injection bores have a diameter of from 0.2 to 2 mm (preferably from 0.3 to 1.2 mm). In addition, the distance between the first injection bores and the second injection bores is advantageously smaller than 2 mm, and preferably smaller than 1 mm.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.